Generally speaking, high purity nickel is required to reduce, as much as possible, alkali metals, radioactive elements, transition metal elements and gas components, and is widely used particularly as a sputtering target material for forming VLSI electrodes and wiring, or for forming magnetic thin films.
Alkali metals such as Na and K easily move within the gate insulation film, and cause deterioration of the MOS-LSI interfacial quality. Radioactive elements such as U and Th cause soft errors of elements with the emitted a rays. Meanwhile, transition metal elements such as Fe also cause trouble at the interface bonding area.
Further, gas components such as carbon and oxygen are not preferable in that they cause the generation of particles during sputtering.
In general, when manufacturing high purity nickel of a 5N level, it is standard to refine the solution through ionic exchange or solvent extraction, and obtain high purification by further performing electrolytic winning or electrolytic refining thereto. Nevertheless, there were problems of inefficiency in that the steps in the method adopting the foregoing solvent extraction process are complex, and it is necessary to give consideration to the safety of the extract agent since a special solvent must be used.
Although it is also possible to consider a relatively simple method of performing electrolysis employing a solution containing nickel upon manufacturing high purity nickel of a 5N level, it could not necessarily be said that the employment of processes such as the foregoing solvent extraction are efficient.